U.S. patent application number 12/516113 was filed with the patent office on 2010-03-04 for method and device for quality management in mammography apparatus.
Invention is credited to Christian Blendl, Karl Lehi Schwartz.
Application Number | 20100054401 12/516113 |
Document ID | / |
Family ID | 38042608 |
Filed Date | 2010-03-04 |
United States Patent
Application |
20100054401 |
Kind Code |
A1 |
Blendl; Christian ; et
al. |
March 4, 2010 |
Method And Device For Quality Management In Mammography
Apparatus
Abstract
The present invention relates to a device and method for quality
management (5) in a mammography apparatus (10), said apparatus
comprising an X-ray source capable of directing a X-ray beam, a
breast immobilization means (16, 18), and an X-ray image sensor
system (20), said X-ray image sensor system (20) comprising a
central area for sensing an image of said breast, and a peripheral
area not used for imaging said immobilized breast. According to the
invention, the device comprises a sensor for quality management
(30), said sensor comprising a radiation dose detector in the path
of said X-ray beam, for producing a dose measurement, and radiation
absorbing elements (130, 350, 360, 380, 390, 400) for producing a
detectable image of said X-ray beam on said X-ray image sensor
system (20), acquisition means (20, 50, 60) for acquiring a digital
image of said breast, and of said sensor for quality management
(30), computing means (70) for computing quality management data
(80) from said digital image of said sensor for quality management
(30), and from said dose measurement.
Inventors: |
Blendl; Christian;
(Bergheim, DE) ; Schwartz; Karl Lehi; (Pyrbaum,
DE) |
Correspondence
Address: |
FITCH EVEN TABIN & FLANNERY
120 SOUTH LASALLE STREET, SUITE 1600
CHICAGO
IL
60603-3406
US
|
Family ID: |
38042608 |
Appl. No.: |
12/516113 |
Filed: |
November 26, 2007 |
PCT Filed: |
November 26, 2007 |
PCT NO: |
PCT/EP07/62832 |
371 Date: |
May 22, 2009 |
Current U.S.
Class: |
378/37 |
Current CPC
Class: |
A61B 6/544 20130101;
A61B 6/547 20130101; A61B 6/0414 20130101; A61B 6/502 20130101;
A61B 6/4233 20130101; A61B 6/583 20130101; A61B 6/542 20130101 |
Class at
Publication: |
378/37 |
International
Class: |
A61B 6/00 20060101
A61B006/00 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 24, 2006 |
EP |
06124777.1 |
Claims
1. A device for quality management for a mammography apparatus, the
device including a sensor for quality management, the sensor
comprising: means for determining dose and/or dose rate of an
exposure to an X-ray beam, the means configured for producing a
first data set readable by a computing means; a plurality of
radiation absorbing elements configured for producing a detectable
image of the exposure to the X-ray beam on an X-ray image sensor
system, a second data set being derivable from an analysis of the
detectable image; and image coding means for producing an
identification code of the exposure on the X-ray image sensor
system, an exposure identification code being derivable from an
analysis of said the detectable image.
2. The device according to claim 1, wherein the plurality of
radiation absorbing elements comprises a plurality of absorbing
plates, each plate having a different thickness, whereby energy of
the X-ray beam is derivable from an analysis of the image.
3. The devices according to claim 1, wherein the plurality of
radiation absorbing elements comprises one or more absorbing
rectangular plates of absorbing material, the rectangular plates
having an angle with respect to an edge of the image sensor system,
whereby resolution of the image sensor system is derivable from an
analysis of the image.
4. The devices according to claim 1, wherein the image coding means
comprises an image coding wheel and a motor.
5. The device according to claim 1, wherein the computer means
comprises: means for acquiring and storing the first data set;
means for acquiring and storing said the detectable image of the
X-ray beam on the X-ray image sensor systems; means for analysing
the detectable image for deriving the second data set; means for
analysing the detectable image for deriving the exposure
identification code; and means using the exposure identification
code for grouping in a quality management data set data of the
first data set and data of the second data set corresponding to
same exposure.
6. The device according to claim 1, wherein the device further
comprises a statistical analysis workstation configured for:
receiving and storing a plurality of quality management data for a
plurality of exposures with the mammography apparatus; and
performing an optimization of working mode of the mammography
apparatus, and/or an optimization of quality assurance of the
mammography apparatus, based on a statistical analysis of the
plurality of quality management data.
7. A method for quality management in mammography, the method
comprising: reading the value of dose and/or dose rate of an
exposure to an X-ray beam, the dose and/or dose rate forming a
first data set; providing a plurality of radiation absorbing
elements producing a detectable image of the exposure to the X-ray
beam on an X-ray image sensor system; providing image coding means
for producing an identification code of the exposure on the X-ray
image sensor systems; acquiring a digital image of the exposure of
the X-ray beam; analysing the digital image for deriving a second
data set; analysing the digital image for deriving an exposure
identification code; using the exposure identification code for
grouping in a quality management data set the data of the first
data set and the data of the second data set corresponding to same
exposure.
8. The method according to claim 7, the method further comprising:
acquiring a third data set, characterizing the mammography process;
grouping in the quality management data set, for each exposure,
data coming from each of the first, second and third data set.
9. The method according to claim 7, wherein the method further
comprises the steps of: storing a plurality of quality management
data for a plurality of exposures with a mammography apparatus; and
performing an optimization of the working mode of the mammography
apparatus, and/or an optimization of the quality assurance of the
mammography apparatus, based on a statistical analysis of the
plurality of quality management data.
10. A computer program product comprising code for executing the
method of claim 7.
11. A system for quality management for a mammography apparatus,
the system including a sensor for quality management, the sensor
comprising: a device configured to determine dose and/or dose rate
of an exposure to an X-ray beam and configured to produce a first
data set readable by a computer; a plurality of radiation absorbing
elements configured to produce a detectable image of the exposure
to the X-ray beam on an X-ray image sensor system, a second data
set being derivable from an analysis of the detectable image; an
image coding device configured to produce an identification code of
the exposure on the X-ray image sensor system, an exposure
identification code being derivable from an analysis of the
detectable image.
12. The system according to claim 11, wherein the plurality of
radiation absorbing elements comprises a plurality of absorbing
plates, each plate having a different thickness, whereby energy of
the X-ray beam is derivable from an analysis of the image.
13. The system according to claim 11, wherein the plurality of
radiation absorbing elements comprises one or more absorbing
rectangular plates of absorbing material, the rectangular plates
having an angle with respect to an edge of the image sensor system,
whereby resolution of the image sensor system is derivable from an
analysis of the image.
14. The system according to claim 11, wherein the image coding
device comprises an image coding wheel and a motor.
15. The system according to claim 11, wherein the computer
comprises: a device configured to acquire and store the first data
set; a device configured to acquire and store the detectable image
of the X-ray beam on the X-ray image sensor system; a device
configured to analyze the detectable image for deriving the second
data set; a device configured to analyze the detectable image for
deriving the exposure identification code; and a device configured
to use the exposure identification code for grouping in a quality
management data set data of the first data set and data of the
second data set corresponding to same exposure.
16. The system according to claim 11, comprising a statistical
analysis workstation adapted for: receiving and storing a plurality
of quality management data for a plurality of exposures with the
mammography apparatus; performing an optimization of working mode
of the mammography apparatus, and/or an optimization of quality
assurance of the mammography apparatus, based on a statistical
analysis of the plurality of quality management data.
17. A method for quality management in mammography, the method
comprising: reading the value of dose and/or dose rate of an
exposure to an X-ray beam, the dose and/or dose rate forming a
first data set; providing a plurality of radiation absorbing
elements producing a detectable image of the exposure to the X-ray
beam on an X-ray image sensor system; producing an identification
code of the exposure on the X-ray image sensor system; acquiring a
digital image of the exposure of the X-ray beam; analyzing the
digital image for deriving a second data set; analyzing the digital
image for deriving an exposure identification code; using the
exposure identification code for grouping in a quality management
data set the data of the first data set and the data of the second
data set corresponding to same exposure.
18. The method according to claim 17, the method further
comprising: acquiring a third data set, characterizing the
mammography process; grouping in the quality management data set,
for each exposure, data coming from each of the first, second and
third data set.
19. The method according to claim 17, comprising the steps of:
storing a plurality of quality management data for a plurality of
exposures with a mammography apparatus; performing an optimization
of the working mode of the mammography apparatus, and/or an
optimization of quality assurance of the mammography apparatus,
based on a statistical analysis of the plurality of quality
management data.
20. A computer program product comprising code for executing the
method claim 17.
Description
TECHNICAL FIELD
[0001] The invention relates to the field of mammography. More
particularly, it relates to a device and method for quality control
of the physical and technical aspects of mammography.
DESCRIPTION OF RELATED ART
[0002] Nowadays, mammography and other radiography examinations are
performed on a regular basis for detecting tumors and other
diseases. A mammography apparatus comprises an X-ray source, a
breast immobilization device, a bucky table and an image sensor.
Traditionally, film screen systems as sensors were used. These
sensor types have the drawback that they need a processing phase
(developing, fixing a.s.o.), and therefore the evaluation of the
results of the examination, and of the quality of the image could
not be performed in real-time. Nowadays, CR (Computed Radiography
using luminescence sensors or storage phosphor plates) or DR
(Digital Radiography, using semiconductor sensors) allow a
real-time evaluation of the quality of the images. Both DR and CR
sensors have a pixel structure, and are provide therefore images
that are not translation- and rotation-invariant.
[0003] The use of mammography is being used for screening
asymptomatic patients is considered justified. Mammography is also
used as follow up during of after treatment (curative mammography).
There is a need to high-quality images for improving the detection
of cancers, and a contradicting need of minimizing the dose to the
patient. Document "European Protocol for Dosimetry in Mammography",
September 1998--EUR 16263--ISBN 92-827-7290.
[0004] For performing quality control of a mammography X-ray
apparatus, it is known to perform daily, weekly, monthly or yearly
quality control checks. These checks are usually performed by
obtaining an image of a test object also known as a phantom, having
different known radiation absorbing characteristics. Some phantoms
have areas of different thicknesses, in a material simulating
breast tissue. Some have elements simulating features to be
detected such as microcalcifications, fibrous structures and
tumours. The CDMAM phantom (Contrast Detail Phantom for
Mammography) is an aluminium plate 0.5 mm thick, having thereon
gold discs of different diameters and thicknesses, embedded in a 20
mm PMMA plate. The CIRS model 011A is an epoxy body, of a size
simulating a compressed breast (length 12.5 cm, width 18.5 cm), and
containing objects simulating defects to be detected.
[0005] DICOM (Digital Imaging and Communications in Medicine) is a
comprehensive set of standards for handling, storing, printing and
transmitting information in medical imaging. It includes a file
format definition and a network communications protocol. DICOM
files consist of a header with standardized as well as free-form
fields and a body of image data. A single DICOM file can contain
one or more images, allowing storage of volumes and/or animations.
DICOM files group information together into a single data set. That
is, a digital radiography image is in the same file as a patient
ID, so that the image is never mistakenly separated from other
information. Mammography apparatuses with DR X-ray image sensor are
known which have an acquisition of the primary voltage in the
transformer of the X-ray tube (kV), the charge through the tube
during exposure (product of current and time, mAs) and entrance
dose data. But the voltage at the secondary of the transformer is
unknown or only estimated or calculated from the primary voltage
and the settings for the transformation ratio. Mammography
apparatuses with CR systems don't get any technical info from the
apparatus into the Dicom header.
PRIOR ART DISCUSSION
[0006] The document US 2004/0202359 describes a method of
evaluation of the quality of a radiographic image. This method uses
a phantom such as the CDMAM phantom ordinarily used in mammography,
comprising an aluminium plate 0.5 mm thick, on which gold chips of
variable diameter and thickness are fastened. However, this method
requires a large phantom for evaluating various statistical
parameters, and therefore cannot be used for assessing the
technical image quality for each breast image in real-time. These
tests with CDMAM Phantom are performed with fixed settings of the
exposure. Other exposures, used in exposing real mammaes can not be
tested or analysed. A proven statistical analysis of all the
different modes of the X-ray apparatuses is not available out of
these tests with CDMAM phantoms or other test devices, such as the
test device described in DIN PAS 1054. With these test devices, an
analysis of the image of the mammae is not performed, neither in
the Fourier space nor or in real space.
[0007] Document DE 19520360 discloses a method for checking
stability of an X-ray generator for diagnostic applications. The
method involves inserting a reference body into the beam path and
switching off the test process when a defined switch-off dose is
reached. The X-ray tube current is measured continuously and the
charge input up to the point of switch-off is determined by
integrating the current over the duration of the test procedure.
The duration of the test procedure is independently measured and a
computer compares these values with those of the initial conditions
and forms differences which are output as a test report. Although
this method allows determining the stability of an X-ray source, it
does not allow performing quality management of other components
and parameters of a radiography apparatus such as image quality,
image contrast, sharpness, noise etc.
[0008] Document WO 2004/049949 discloses a mammography method and
apparatus wherein information about breast immobilization paddles
position, force, and duration are provided, together with other
X-ray source pulse information, and manual input of data, to a
tissue exposure control calculator that computes and displays
technical factors for an X-ray exposure, such as X-ray tube
voltage, X-ray tube current or exposure time. However, no means are
provided for ascertaining the quality of the image, and for
acquiring and storing the actual dose to the patient.
[0009] It is an object of the present invention to provide a device
and method for quality management in a digital mammography
apparatus which aims to overcome the above discussed disadvantages
of the prior art. It is desired to improve the quality management
of each exposure, for ensuring the quality of the patient clinical
results, as well as minimizing the dose to the patient. It is also
desired to improve the quality management of the apparatus used for
performing these examinations, and to save time in the daily,
weekly, monthly or yearly QA tests with test devices.
SUMMARY OF THE INVENTION
[0010] The present invention is related to a device and a method
for quality management for a mammography apparatus, as well as a
computer programme product as described in the claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 is a schematic view of a mammography apparatus known
in the art.
[0012] FIG. 2 is a top view of a bucky table for use in a
mammography apparatus, wherein a sensor for quality management
according to the invention is installed.
[0013] FIGS. 3a and 3b are bottom and top views of a sensor for
quality management for use in the invention.
[0014] FIG. 4 is a schematic view of device for quality management
for use in a mammography apparatus.
[0015] FIG. 5 is an example of a plot used for statistical analysis
of the quality management data.
DETAILED DESCRIPTION OF THE INVENTION
[0016] According to a preferred embodiment, the invention is
directed to a device for quality management in a mammography
apparatus. The mammography apparatus comprises an X-ray source
capable of directing a X-ray beam, a breast immobilization means,
i.e. a compression paddle and a bucky table, and an X-ray image
sensor system. This X-ray image sensor system comprises a central
area for sensing an image of said breast, and a peripheral area not
used for imaging said immobilized breast. The device comprises:
[0017] a sensor for quality management said sensor comprising a
radiation dose detector in the path of said X-ray beam, for
producing a dose measurement, and radiation absorbing elements for
producing a detectable image of said X-ray beam on said X-ray image
sensor system; [0018] acquisition means for acquiring a digital
image of said breast, and of said sensor for quality management;
[0019] computing means for computing quality management data from
said digital image of said sensor for quality management, and from
said dose measurement.
[0020] In a preferred embodiment, the device comprises a
statistical analysis workstation for storing a plurality of quality
management data for performing an optimization of the working mode
of the mammography apparatus, and/or an optimization of the quality
assurance of the mammography apparatus.
[0021] Preferably, the computing means comprise means for providing
a formatted file comprising the digital image of said breast,
associated with corresponding quality management data. The
formatted file can be formatted according to the Dicom
standard.
[0022] The quality management data may contain one or more of the
following data: [0023] the dose measured by the sensor for quality
management [Gy]; [0024] the dose rate provided by same sensor
[Gy/h]; [0025] the exposure time; [0026] position number of angular
position of coding disk; [0027] the thickness of the immobilized
breast [mm]; [0028] the actual energy [kV] of the X-ray beam;
[0029] distance from the edge of the X-ray image sensor system to
the side `A` of the breast immobilization means; [0030] angular
mismatch between an edge of the X-ray image sensor system, and the
side `A` of the breast immobilization means; [0031] the
signal-to-noise ratio (SNR); [0032] contrast-to-noise ratio (CNR);
[0033] modulation transfer function (MTF); [0034] the beam quality
(HVL); [0035] the expected energy [kV] of the X-ray beam; [0036]
the average glandular dose, calculated by the mammography
apparatus, AGDma; [0037] the current in the X-ray tube; [0038] the
compression distance between the compression paddle and the bucky
table; [0039] the product of the X-ray tube current and the
duration of the irradiation, i.e. the charge through the X-ray tube
during the irradiation [mAs]; [0040] the average glandular dose
calculated by the quality management device, AGDqm; [0041] the
patient identification data and age; [0042] the X-ray source
voltage [kV]; [0043] the spatial resolution; [0044] the threshold
contrast visibility.
[0045] According to a preferred embodiment, the invention relates
to a method for quality management in mammography comprising the
steps of: [0046] providing a sensor for quality management in the
path of an X-ray beam; [0047] acquiring a digital image of an
exposure of a patient breast, and of said sensor for quality
management; [0048] computing a second data set from said digital
image of said sensor for quality management.
[0049] The method preferably further comprises the steps of: [0050]
acquiring a first set of technical data from said sensor for
quality management; [0051] acquiring said second set of technical
data set; [0052] acquiring a third data set, characterizing the
mammography process; [0053] grouping in a quality management data
set, for each exposure, the data coming from each of the first,
second and third data set.
[0054] The method, more preferably, comprising the steps of [0055]
storing a plurality of quality management data for a plurality of
image exposures with a mammography apparatus; [0056] performing an
optimization of the working mode of said mammography apparatus,
and/or an optimization of the quality assurance of said mammography
apparatus, based on a statistical analysis of said plurality of
quality management data.
[0057] According to a preferred embodiment, the invention provides
a sensor for quality management in a mammography apparatus,
comprising one or more of the following components; [0058] means
for determining dose and dose rate of an X-ray beam; [0059] means
for determining energy of an X-ray beam; [0060] means for
determining the resolution of an X-ray image sensor system; [0061]
means for identifying a specific image exposure in a sequence of
successive image exposures taken with a mammography apparatus.
[0062] means for defining the geometrical position of an X-ray
image sensor system in respect to a bucky table;
[0063] Preferably, in the sensor, the means for determining the
resolution of an X-ray image sensor system comprise a square plate
and/or a rectangular plate, said plates being made of a radiation
absorbing material, said plates having an angle with respect to a
edge of said sensor.
[0064] In a preferred embodiment, the invention provides a computer
program product comprising code for executing the methods and/or
for cooperating with the devices and/or the sensors of the
invention.
[0065] FIG. 1 is a general schematic view of a known mammography
apparatus 10. A structure 12 carries a first arm 14 on which an
X-ray source is installed. A second arm carries a breast
compression paddle 16, and a third arm carries a bucky table 18,
also known as a breast tray. An X-ray image sensor system 20
receives X-rays emitted from the X-ray source after passing through
said compression paddle 16 and patient breast. All three arms are
moveable along the structure 12, and this structure may in turn be
moveable in translation and rotation movements. All these movements
are controlled by an operator so as to give the optimal geometry,
depending on patient size, etc. Means are provided for measuring
and acquiring the distance between the compression paddle 16 and
the bucky tray 18.
[0066] FIG. 2 is a top view of a bucky table 18 for use in a
mammography apparatus. The patient thorax is applied along side
`A`, with a breast above the table 18. Inside or below the tray 18,
an X-ray image sensor system 20 is installed. This imaging device
may be an electronic sensor, such as a flat panel, also called DR
(Direct Radiography) or a luminescence foil, also called CR
(Computer Radiography). According to the invention, a sensor for
quality management 30 is installed in an angle of the breast tray
18 located near the supporting arm and structure 12, i.e. away from
the side `A` where a patient breast is introduced in the apparatus.
By selecting this location, the sensor for quality management 30 is
located in an area of the image sensor that is not used in a
patient mammography. The sensor for image quality management of the
invention 30 comprises at least one of the following elements:
[0067] means for determining dose, dose rate of the X-ray beam
and/or exposure time; [0068] means for determining energy of the
X-ray beam; [0069] means for determining the resolution of the
X-ray image sensor system 20; [0070] means for identifying a
specific image exposure in a sequence of successive image exposures
taken with a mammography apparatus; [0071] means for determining
the geometrical position of the X-ray image sensor system 20
relative to the bucky table 18; [0072] means for determining the
time of exposure (time stamp). Each of these elements is discussed
in more detail in the following paragraphs.
[0073] Referring to FIG. 2, the sensor for quality management 30
comprises a box 200. In this box 200, made of an X-ray transparent
material, a set of three stacked diodes or other dose measurement
device, such as ionization chamber, is installed. A set of
radiation absorbing filters of different attenuating materials and
thicknesses are installed above each of the detectors. These filter
elements are chosen so that the filters exhibit different radiation
absorption characteristics within the given voltage range. The
diodes receive the attenuated radiation as it passes through the
different filters and provide signals of different magnitudes. The
ratio of the signals from the diodes at any instant in time is a
function of the X-ray tube voltage (kVp) at that time, and thereby
gives the energy of the X-ray beam. The signal from each detector
can also be integrated over the exposure time and then the ratio of
the integrated signals taken. This provides a different measure of
tube potential, kV. This principle of kV detection of X-ray systems
is well known in the art in a variety of stand alone meters. Also,
the electronic components for transmitting the measured dose, as
well as other acquired technical data, are installed in this box
200. The total dose of a single exposure can be recorded, as well
as the dose rate (i.e. dose per unit time) and the exposure
time.
[0074] The FIG. 3a is a bottom view of the support plate 330 for a
sensor 30 of the invention. The sensor for quality management 30
comprises the following components: a support plate 330 for
supporting different test objects. This support plate 330 is a 2 mm
tick plate made of an X-ray transparent material, such as carbon
fibre reinforced plastic. In the bottom side of this plate, three
hollows are provided for containing three aluminium plates 380,
390, 400, having a thickness of, respectively, 0.3, 0.5 and 0.7 mm.
By measuring the X-ray absorption of these plates 380, 390, 400 on
X-ray image sensor system 20, one can determine the Half Value
Layer (HVL). The HVL is the thickness of aluminium-equivalent
absorber which attenuates the air kerma of an X-ray beam by half.
From the HVL, the energy of the X-ray beam can be determined by
known techniques. This measurement of the energy can be compared
with the energy value obtained from the stacked diodes in box 200.
From the comparison of these two energy measurements, a quality
assurance of the mammography apparatus and method is obtained.
[0075] Referring to FIG. 3b, two hollows are provided on the top
side of support plate 330. Thin rectangular plates 350, 360 of
absorbing material are laid in these hollows. These hollows are
slightly inclined with respect to the X-Y axis of the imaging
device underneath. An angle of 2.degree. is appropriate. By
analyzing the image produced, one can determine the Modulation
Transfer Function (MTF), and thereby, the resolution of the
apparatus. A square 350 and an elongated rectangle 360 are used.
Both are made of a strongly absorbing material such as iron (Fe) or
tungsten (W) having a thickness of at least 1 mm. A pattern 365 of
a material with a high atomic number, e.g. lead (Pb), molybdenum
(Mo) or tungsten (W) is used to offer the possibility to check the
visual resolution. One type of the available pattern which is used
contains groups of lines pairs with 8, 10, 13 and 16 line pairs per
mm (Lp/mm). The size of the pattern is about 15 by 15 mm. The other
pattern which is available is made as a star pattern with an
diameter of about 15 mm. By analysing the star pattern, an
irregular pattern in the core of the pattern is achieved in which
no resolution is detectable. An enlargement of this area of
unsharpness indicates an enlargement of the size of the focus. This
enlargement could be one or bidirectional.
[0076] Referring to FIG. 3b, one hollow is provided on the top side
of support plate 330. A thin square plate 350 of absorbing material
is laid in this hollow. This hollow is perpendicular with respect
to the X-Y axis of the bucky table 18 underneath. By analyzing the
image produced by this square plate 350, one can determine the
geometrical position of the X-ray image sensor system 20 relative
to the bucky table 18, and thereby, the non imaged breast area
caused by the distance between the edge of bucky table 18 and the
X-ray image sensor system 20. This square plate 350 is made of a
strongly absorbing material such as iron (Fe) or tungsten (W)
having a thickness of at least 1 mm.
[0077] Referring to FIG. 4, the image data, acquired by X-ray image
sensor system 20 are sent directly to a image viewing workstation
60 for direct observation. In the case of DR images, these data are
sent directly. In this case, the link between the acquired
technical data 40 and the acquired image data 45 is made simply by
the fact that they are acquired simultaneously. When using a CR
imaging system, a manual operation of reading the CR cassette is
performed in a CR cassette reader 50. This manual operation breaks
the simultaneity of acquisition of the acquired technical data 40
and the image data 45. Moreover, the operator could process
successive CR cassettes in a order different from the order of
exposure. Therefore, a means for identifying each successive CR
image has been devised as follows: The sensor for quality
management 30 is provided with an angular coding disk. Such angular
coding disks are well known in other applications. They comprise,
at different radiuses on the disk, sectors marked in a recognizable
way. The radiuses and sectors are selected such that, by examining
the image on a radius of the disk, the angular position of the disk
can be determined. In the present application, the sector are
marked with a radiation opaque material, and a radiation
transparent gap is provided so that a coding of the angular
position, among twenty distinct angles, can be detected on an image
acquired through the X-ray image sensor system 20. A motor 140 is
provided in the box 200. This motor rotates disk 130 from a
determined angle (i.e. 18', for a 20 position disk) for each
successive exposure.
[0078] The device for quality management of the invention is
represented in FIG. 4 as a block diagram. A first set of acquired
technical data 40 is sent directly from the sensor for quality
management 30 to a data processing device 70: [0079] the dose
measured by the sensor for quality management 30 [Gy]; [0080] the
dose rate and/or exposure time provided by same [Gy/s]; by plotting
successive values of the dose rate during an exposure, a waveform
of the X-ray intensity is obtained. [0081] the exposure time;
[0082] position number of angular position of coding disk. A second
set of data 41 is determined from an analysis of the image data,
being either the acquired DR image 45, when using a DR-sensor, or
the acquired CR image 46 when using a CR-sensor and a CR cassette
reader 50. In both cases, an analysis is performed in an image
viewing workstation 60, and provides the following second set of
data: [0083] the actual energy [kV] of the X-ray beam is determined
from the image area showing the three aluminium plates 380, 390,
400; [0084] position number of image of coding disk; [0085] The
distance from the edge of the X-ray image sensor 30 to the side `A`
of the bucky table 18 where a patient breast is introduced; [0086]
Any angular mismatch between an edge of the X-ray image sensor
system 20, and the bucky table 18; [0087] Different Signal-to-noise
ratios (SNR) (behind each Al filter the SNR can be calculated);
[0088] Different Contrast-to-noise ratio (CNR) (between two Al
filters the CNR can be calculated); [0089] Modulation transfer
function (MTF) as a scientific value of the Spatial Resolution the
used material of the anode and the additional filter calculated
with the Al-HVL (Aluminium Half Value Layer) and the dose rate to
calculate the Mean Glandular Dose (MGD). [0090] Beam quality
(Al-HVL); The last parameters are determined from the image area
showing the square 350 and an elongated rectangle 360 using methods
known in the art, as stated e.g. in PAS 1054 or to IEC 61223-3.
This second set of data is then sent from image viewing workstation
60 to data processing device 70. A third set of data 42 is provided
by the mammography apparatus 10 itself to the data processing
device 70: [0091] the expected energy [kV] of the X-ray beam, as
determined by the primary voltage of the X-ray tube power supply
and the setting of the ratio of the transformer used; [0092] the
average glandular dose, calculated by the mammography apparatus,
AGD.sub.ma in a way well known in the art, based on patient age,
machine settings for kV and mAs, thickness of the compressed
breast, and anode-filter combination; [0093] the current in the
RX-tube [mA]; [0094] the compression distance between compression
paddle 16 and the bucky table 18. This last data may be provided by
a special sensor added to the mammography apparatus. The
measurement device for the compression distance may comprise a
magnetic incremental lift encoder and a scanning sensor. The
scanning sensor is mounted on the compression paddle support (16)
and a magnetic tap is installed on the guide rail of the
mammography apparatus. Depending on the compression distance, the
scanning sensor generates counter pulses (TTL Signals) and the
conversion of pulses is representative for the compression
distance.
[0095] The device for quality management of the invention comprises
a data processing device 70 performing the following functions:
[0096] grouping in a single record, the quality management data set
80, for each exposure, the data coming from each of the first 40,
second 41 and third 42 data set; [0097] determining and adding to
the record the following data: [0098] the product of the tube
current and the duration of the irradiation, i.e. the charge
through the tube during the irradiation [mAs]; [0099] the average
glandular dose calculated by the quality management device, AGDqm,
based on the same parameters as above, but taking the acquired
values of these parameters; [0100] patient identification data and
age; [0101] the irradiation duration [ms]; This record is
preferably organized as a DICOM-compliant record, and contains all
above cited-data, as well as the image of the exposure. This record
is sent by the data processing device 70 to the statistical
analysis workstation 90.
[0102] The device for quality management of the invention also
comprises a statistical analysis workstation 90 This workstation
stores all successive quality management data sets 80. Acquiring
and storing the quality management data 80 together with the image
data for each exposure allows the statistical analysis of this set
of data for attaining the following purposes: [0103] optimize the
working mode(s) of the mammography apparatus; [0104] optimize the
quality assurance of the mammography apparatus. The optimization of
the working mode of the mammography apparatus is performed as
follows: a data A, related to a data B are plotted in a linear
regression plot exemplified on FIG. 5, where values A, B of an
exposure are represented by a point. Points are scattered around a
regression line. The statistical analysis entails the observation
of points X that are beyond the 2 .sigma. line around regression
line. The occurrence of such points is an indication of some
malfunction of the mammography apparatus. If a representative point
of the exposure of the patient currently being examined lies beyond
the 2 .sigma. line, a conclusion may be drawn that something went
wrong in this exposure. The working parameters of the mammography
apparatus may then be adapted for correcting the default. On the
other hand, by analyzing the statistical results of a large number
of exposures, on may observe that the 2 .sigma. line lies two far
away from the expected values. In this case, a malfunction of the
apparatus may be inferred. Among the couples of data A, B that may
be used for such statistical analysis are the following couples,
listed as examples: 1) Couples, which are used to control values
given by the apparatus: [0105] exposure time: to control changes in
triggering the signals; [0106] dose rate: to detect changes in the
surface of the anode, which lowers the dose rate and/or the dose
yield (Dose per mAs). These changes can not be detected by
calculated values. [0107] Tube Voltage [kV]: to detect changes in
the surface of the anode, which change the beam quality (beam
hardening) and which can not detected by calculated values. The
expected tube voltage (kV of the X-ray beam, as determined by the
primary voltage of the X-ray tube power supply and the known ratio
of the transformer, and the actual voltage [kV] of the X-ray beam
as determined from the image of the three aluminum plates 380, 390,
400 and/or measured by the (Wellhofer device); [0108] Thickness of
compression of the breast: both measurements influence the
calculation of the Average Glandular Dose 2) Couples or values,
which are used to analyse the exposure technique or to analyse
technical values of each exposure in respect to others. [0109] age:
to control the age restrictions, which are made in screening
programs; [0110] Paraphe of the technician: to control the used and
statistically analysed compression force of each technician and to
harmonise the compression force to best practice between all
technicians. [0111] The Average Glandular Dose, as calculated by
the mammography apparatus, AGD.sub.ma, and the average glandular
dose as calculated by the quality management device with measured
datas: to control the AGD.sub.qa in respect to legal restriction
and to correlate the AGD.sub.qa with the exposing values for each
individual breast to analyse and optimize the used exposure
technique (ALARA-Principle) [0112] The Exposure Index, as
calculated by the quality management device or by the mammography
apparatus is based on the histogram of the image and can be used to
control the dose at detector plane. [0113] Signal to Noise Ration
(SNR) or/and Contrast to Noise Ratio (CNR)), calculated in the
image in correlation to other values, which describe the measured
beam quality: these correlation can be used to differentiate
between noise sources: beam quality or detector. 3) Values, which
are produced by an analysis of the image of the mammae itself and
which can correlate with the morphological composition (fat versus
glandular tissue), the absorbing characteristics of different
tissues, the used exposure technique and/or clinical diseases.
These analyses with resulting values are a part of the quality
management system. Some examples of applicable image processing
methods are listed below: [0114] histograms: deviations from an
averaged histogram is useful; [0115] frequency pattern: A Fourier
analysis from each image shows the frequency content of a
mammogram. Significant deviations from an averaged frequency
spectra is useful. [0116] noise power spectra: significant
deviations from an averaged spectra is useful. The statistical
analysis performed on the data is similar to the statistical
process control (SPC) method used in manufacturing industries for
achieving quality control.
[0117] Although FIG. 4 represents image viewing workstation 60,
data processing device 70, and statistical analysis workstation as
separate computers, this is not required by the invention. Two of
these computers, or all three may be grouped in a single one
performing all the functions discussed. An integrated, single
workstation may be preferred for a new mammography apparatus, while
the separate design shown in FIG. 4 may be preferred for
retrofitting the device for quality management of the invention to
an existing mammography apparatus.
[0118] By using the device and method of the invention, the actual
diagnostic image and the quality assurance data are collected in a
single exposure. Thereby, no weekly or daily QA tests are needed
any more. The monthly and yearly QA test are shortened to tests
which can be performed in a few minutes or a few hours
respectively, and quality assurance data are obtained in real time.
In addition, these meta-data are stored, together with the image
data, in a Dicom data file, thereby ensuring that all the relevant
data are available for evaluation by a medical physicist or expert
at a later time.
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